Carburetor



May 25, 1948.

S. F. HUNT CARBURETOR Filed June 17', 1943 EE TTFHL/NT Patented May 25, 1948 CARBURETOR Scott F. Hunt, Meriden, Comi., assignor, by mesne assignments, to Niles-Bement-Pond Company, West Hartford, Conn, a corporation of New Jersey Application June 17, 194a'seriai is. 491,096

This invention relates to carburetors for internal combustion engines, and particularly to means for operating such carburetors so as to provide improved acceleration characteristics of throttle, and effective upon an increase in such pressure, such as accompanies a sudden opening movement of the throttles, to inject into the air stream an additional supply of fuelso as to rapidly accelerate the engine.

It has been found that with devices of the type described, the additional supply of fuel provided is not always suificient to complete the acceleration of the engine to a speed corresponding to the new throttle position. Such a device provides a momentary additional supply of fuel for the engine, but it has been found that this additional supply of fuel may be completely dissipated before the acceleration of the engine is completed.

It is therefore an object of the present invention to provide improved means for supplying additional fuel to an internal combustion engine during acceleration of the engine,

A further object of the invention is to provide an improved fuel supply system for an internal combustion engine wherein a first device is used to give an increased fuel supply immediately in response to acceleration of the engine, and a second device is used to provide another additional fuel supply after a time delay following the initiation of a period of acceleration.

A further object of my invention is to provide a device of the type described wherein the valve which normally controls the fuel supply to the engine is utilized during periods of ac--* celeration to supply an additional amount of fuel to the engine.

Another object of the present invention is to provide an improved carburetor of the'type in which the fuel flow controlling valve is operated by fuel pressure controlled by a pilot valve, in which means are provided to increase'the pressure on the fuel flow controlling valve in response to acceleration of the engine on which 4 Claims. ((11.261-69) which operates cumulatively in response to the increasedfuel supply to further increase the supply of fuel.

A further object of the invention is to provide an improved pressure controlling device which is balanced against the controlled pressure so that upon the application of a force to the pressure controlling device, it operates throughout its range of movement, without being retarded by changes in the controlled pressure.

A further object of the invention is to provide, in acarburetor having a throttle controlling the flow of air, means responsive to the pressure downstream from the throttle for supplying additional fuel. to the engine upon acceleration thereof, and means for balancing the pressure responsive means against changes in atmospheric pressure.

Other objects and advantages of the present invention will become apparent from a consideration of the appended specification, claims and drawing, in which The figure illustrates, somewhat diagrammatically, an aircraft carburetor embodying cer tain principles of my invention.

.In thedrawing there is shown at In the main body portion of an aircraft carburetor including an air passage l l, through which the air flows from'an. entrance [2 to an outlet l3 which connects, by means not shown, to the intake of a supercharger by which the air is forced into the engine under pressure.

The fuel supply for the engine comes from a pump or other source of fuel under pressure, and passesthrough a conduit M, a vapor trap IS, a conduit IS, a fuel regulator unit 11, a conduit I 8, a second vapor trap 20, a mixture control unit 2|, a jet system generally indicated at 22, a conduit 23, an idling control 24, a conduit 25, a pressure regulator .26, and a passage 2! to a fuel injection unit, not shown. The fuel injection unit may preferably be of the type known as a spinner injector, wherein the fuel is introduced into the 'air stream through suitable orificesin the rotor of the supercharger.

The carburetor I0 may be of the rectangular type shown in the U. S. Patent No. 2,361,993, issued to Milton E. Chandler on November 7, 1944.

j' Near the air entrance l2 of the carburetor a pluinto the'carburetor. into a passage 3| which interconnects all the rality of impact tubes 30 project into the air stream, with their ends open in a direction to receive the dynamic pressure of the air flowing These impact tubes open impact tubes, and is commonly termed avent provided with apertures 4| at or near the point of smallest cross section of the passage H.

It will be seen that the pressureat the. impact 5 tubes 30 is higher than the pressure at theaper tures 4| in the Venturi memberslkandthat, in accordance with the well known characteristics from. the ex pansible chamberwifi, which serves astne outlet chamber of the valve and is connected to the conduit l8. A tension spring 6| is attached to the lower end of valve member 53 and to a nut 82 carried by a bolt 33 which threadedly engages an aperture in -the bottom of the casing of regulator ii. The lower extremityof the nut 53 is provided with an hexagonal head 54 by which it may be turned to adjust the tension in the spring 5|. A look nut 65 1s provided to maintain the bolt 63 in any position The chamber as is connected through a pas: sagett arestriction 67 therein to the of Venturi meters, this pressuredifierential. is a.

function of the velocity of the air flowing through the passage Because of this pressurgdifiera ential, a continuous flow of air takes place through a. second air-passage, which may be traced thru the. impact tubes-3U, the vent ring 3 l,

the conduit 32, chamber 33, boost venturi 34;

valve 35, chamber 36, conduit 38, the interior of the Venturi members 40, and -out through the to which it may be adjusted.

interior of chamber 55. Chamber 45 is connected through a conduit 33 having a restriction 1E3 thereintothe conduit adjacent the pres-- sure regulator 26.

A pair of discs 13 and ii are clamped, by any suitable means, on opposite sides or a central aperture. in the'diaphragm 5!. A force transmit ting member .12 iscarried by the discs '16 and H a apertures 4| into the main air stream, Although the pressure difierential acrossthe second. air

passage is a function of the velocity oithe air il'owingin-thamain. air passage l', the air now thru the second air passage is controlled. by the, valve 35, as hereinafter described, so that the velocity of the airflow thru the second passage unit is a measure of the mass of air flowing per time thru the main air-passage The-boost venturi 34 is provided with anannularopening 42' at its throat, Theopening 4.2

communicates through suitable passages with a conduit 43. In accordance with the known characteristics'oi' Venturi meters, the pressure at the opening 42 is lower than the pressure at the openings 4|, and the diffierential between the pressures at the impact tubes 33 and the pressure .at the opening 42 is a measure of the velocity .orair flow through. the second air passage previe ously traced. It may, thereiore be seen that the boost venturi 34. provides .a. pressure differential is-a measureof the mass. of flowing reru it time. through the main p ss e H, but fwhichis. larger-than the pressure difierential whichwould. be obtained by means of a single.

bers'40. r a V r The pressure at. the impact-tubes 33 is. conveyed. through-vent ring 3| .and.conduit 44 to tuelregulator'unit-l'l; The pressure at the venturi arrangement. such as the Venturi memopening 42 in, the throat. of boost venturi 34' is conveyed through. conduit 43130 the iuel regulater unit l|,;where these two pressures are compared. order to produce a controlling. force proportional to the difference betweenthem.

The-fuel. regulator f1 comprises a hollow casingnwhich. divided into a series of four exand extends theret'hrough. The lower part ofthe I force transmitting member if is provided witha fiat surface, which is adapted to engage a con- .vex surfaceat the upper end of Valve member '53.". Another force transmitting member 13 is.

similarly attached to the central portion of the diaphragm 53.. The upper surface of the m'eniber. T2. is recessed to receive and cooperate with a guiding projection'l i onthe lower end of the member 13. The upper surface of the member pansible -chambeijs 45,-. 46,41 and 48.by' means of'threefiexiblediaphragms 5.3,. 5|. and. 52'. The

outer peripherieslof diaphrag nis5|!r SI, and 52. -areattached to'the-casing of the regulator unit H ran? itab e. means, not sh wn.

j A balanced. valve member 53 is supported cenally-o th di p raem 52.1.1.1 a rsuitahle man I l==. V lve'53 provided a. pair of fian cs' and 55-.) which cooperate respectively with stationaryvalves ats 56 a dil. which may beformedin th casin of the regulator H,

" W en valve. 53 ia...seeted, iii-sep es. an. inlet: chamber fidconnectedto the conduit; 16,

i3 is similarly recessed to'receive and cooperate,

with a guiding projection "55 which is rigidly attached. to the casing'of. the regulator IT.

.The amount of fuel fiowing .throughthe jet system .22 at, any giventime is proportional to the pressure drop across that system. .It is de sired that this fluel flow be proportioned to the flow of air through the air passage I. 'As previously described, it may b seen that the pressure at theimpact tubes 33 is communicated through the vent ring 3| and the conduit 54 to the chamber 46 in the regulator i'i. It has likewisebeen pointed out that the very low pressure at the throat of the boost venturi 34 is conveyed through the conduit 43 to the interior of chamber. 41.; The d'ifier'ence in. pressures between chambers 45 and 47'. produces a force acting downwardly on the discs to and 7| and the. force transmit ting member '52, and thereby tending to open valve member 53. This force is ameasureof the mass of' air "flowing per unit. time through 7;

passage 1 i The pressure in the chamber 36 may be'considered as being, equal to, or atleast indicative of, the pressure at the intake side ofthe'jet system 22- Furthermore, the pressure in the chamber 45 issubstantially equ'al' to'that existing in the conduits 53 and 25 the discharge side. of the jet system 2 2. The pressure inchamber 45 is less than the pressure in chamber .48 and the differential between these two pressuresiw exerts:- through the force transmitting members: 7 l2 and 3 a force tending to close valve mem-' ber 53. v i 7 v It may be stated that the differential between; the pressures in the chambers 45 and 47 exerts anopening force on the valve, 53 which is a j function of the mass of air flowing through the v carburetor per unit time: and' that the difier-J, ential between the pressures'in' the chambers;

t5 and iitexerts a closing forcef on the valve 1 '53,. which is a iunction of the mass of fuel flowing tothecarburetor. The pfosition of valve f member 53 at any time is determined by the position it must assume to balance the force produced by the pressure differential across the jets against the force produced by the pressure differential which measures the air flow through 5 the passage II.

. Proper combustion conditions are attained when the mass of the air supplied to the engine is properly proportioned with respect to the'mass of the fuel. Since the fuel density is substantially constant, the pressure differential across the jets, which is a direct measure of the volume of fuel flowing, may be taken as a measure of the mass of the fuel without introducing appreciable error. However, the density of the air flowing through the passage II varies with atmospheric pressure and with the air temperature, and hence it is necessary in measuring the air flow to correct for variations in air temperature and pressure in order that the metering force produced by the chambers 48 and 4! may accurately reflect the mass of the air flowing through the, passage I I rather than its volume. This cormotion is made by the valve 35, which is operated by a bellows I35 mounted within the housing 3l. One end of the bellows I35 is fixed to a screw I36, which threadedly engages the housing 3-1; so that the positions of the bellows I35 and the .valve 35 with respect to the housing may be'adjusted. The bellows I35 is preferably filled with nitrogen or other inert gas. Then as the pressure in the chamber 33 varies with the altitude of the aircraft, or from other causes, the *changein pressure causes an expansion or contraction ofbellows I35, thereby operating the valve 35 to restrict the air flowing through the .boost venturi 34 to a greater or less degree. Likewise, changes in the temperature of the flow- .ing air cause a responsive movement of the bel lows I35 to operate the valve 35.

.,-- 'Ihe atmospheric pressure and temperature operated valve 35 is used to throttle the flow of fluid thru the boost venturi. While the pressure -'diiferential between the throat of the boost ven- -turi 34 and the vent ring 3i is not a measure of the velocity of the fluid flowing thru. the passage -I-I.because of the throttling action of valve 35, it will be readily understood that by properly forming the valve 35, it may be made to compensate for variations in air density so that the pressure differential referred to accurately measures the mass of air flowing thru the passage I I. -Since,:in a carburetor, it is desired to proportion the mass of the fuel to the mass of the air, it -will'be seen that this arrangement of the boost venturi 34' and valve 35 contributes to that result. inasmuch as the force applied to the diaphragm SI of the regulator unit I! is thereby made proportional to the mass of the air supplied to the carburetor.

Since the capacity of the annular opening 42 in the throat of the boost venturi 34 is quite small, it is necessary that the chambers 41 and 46 be separate from each other, as even a small air' passage between them would be suflicient to I .appears in the drawing to be near the topof that in the chamber 46.

-chamber, but it should be understood that this is only for purposes of convenience inmaking the drawing and that in actual practice the drain tube I40 would be connected at the lowest point Each-of the vapor traps I5 and 20 consists of a chamber, such as IS in trap I5, normally filled with fueland having a valve 11 in the upper portion thereof controlled by a float I8 so that the valve is closed as long as the chamber remains filled with liquid fuel. If the fuel vaporizes, the

bubbles of vapor rise to the surface of these traps whereupon the float is lowered opening the valve so that the vapor may be drawn off through the opening normally closed by the valve. Each valveis provided with a sleeve 19 which operates to close the entrance ports of the valve in case the vapor trap is inverted, such as might occur when the aircraft is flying up side down. The vapor trap I5 is provided with a screen for filtering the incoming fuel.

The mixture controlling unit 2| includes a disc valve 90, which is rotatable by a shaft 9| on which it is fixed. The disc valve is provided with suitable ports so that it may be positioned to permit a fiow of fuel from'the conduit I9 through either a conduit 92 alone or through the conduit 92 and a parallel conduit 93. When the fuel is flowing through the conduit 32 only, the mixture conduit 93 is connected with a jet 99.- The jets 99 and discharge through another jet 91, and

the jets 94'and Ill discharge directly into the conduit 23.

The conduit'23 conveys the fuel to the idling control 24 which includes a jet 98. A valve member I00 is in the position shown in full lines in the drawing whenever the engine is running throttles I02 positionedin the main air passage I I. This idling control-valve I00 cooperates with spring BI to control the fuel flow under low air 'fiow'c'onditions. Under'such conditions, the air flow metering mechanism is unreliable because of the very low flow as compared to the large crosssectional area of the air conduit. Therefore, the

spring BI is provided to bias the valve 53 open.

The valve opening force of spring 6| is opposed by the fuel pressure differential across the jet system tending to close the valve. Theresult is that a substantially constant fuel pressure differential is maintained (when the air pressure diiferential is negligible), whose value is determined by the tension of spring 6I. Having such aconstant fuel pressure difierential, the fuel flow may then be determined by the contour of the idle valve I00 and the throttle position. In this way, a positively controlled fuel flow is obtained under idling conditions, even though the pressuredifierential set up by the air venturi is small and erratic.

The pressureregulator' 26' comprises a housing divided into two chambers by a flexible diaphragm 13. A pair or discs-M4 and HlSare clamped to the central portion of the diaphragm I03, in any suitable manner;

26 so as tobloclr the passage 21 when the valve is closed. The chamber above the diaphragm I-'3 is vented, through a passage I08 to the conduit 43, wherein the pressure is considerably below atmospheric. Since the pressure in conduit the engine is'in operation, the pressure difierential on opposite sides of the diaphragm I03. is such as to maintain the valve I01 open. against the compression of spring MB. The pressure in the chamber above diaphragm I03 is so small compared to the pressure in the chamber containing valve 101 and the force of the spring I06, that that small pressure exerts no appreciable controlling effect on theregulator. The low pressure above the diaphragm Hi3 does, however,'

provide a differential pressure for opening the valve I01. The. spring I06 opposes the pressure in the chamber belowgthe diaphragm I 03, and

operates the valve in a'manner to maintaintha pressure substantially constant.

' -A primary acceleration responsive regulator I I0 is shown as being mounted on the wall of the we 7 carburetor body Ill below the throttles I02; The

regulator Il'B- consists of a hollow casing divided intotwo chambers by a flexible diaphragm III. A valve stem H2 is supported centrally of the diaphragm II I, and-carries at its left hand end avalve H3; A conduit I 65 connects an annular chamber I I4 adjacent the valve stem with the conduit I6 which isr connected to thersource of fuel under pressure. When the valve H3 is in the position shown, it cutsoff the flow of fuel from the chamber I I4 into'the main air passage II; The chamber to the left of, thediaphragm in in the casing I Ill is sealed from the annular space surrounding the valve. stem H2 and is connected with the outlet l3 of the main air passage IIby means of a conduit Ill. The chamber onthe right hand side of diaphragm III is connected to theoutlet [3 through a conduit I I8 having a restriction I25 therein. A compression spring I2I biases the'va1ve'Il3 to closed position.

As long as the air flow through the outlet ,I3 remains substantially constant, the pressures in the chambers on opposite sides of the diaphragm Ill are substantially equal, sathat the valve H3 is held closed by the compression spring l2.I-.

Upon. a sudden opening'movement of the throttles I02- such as accompanies asudden acceleration of the engine, "the consequent sudden increase in pressure inthe airpassage II is communicated to the chamber at the left of dia-i 'phragm' III more'rapid'ly than to the'chamber at the right, because of the restriction I20.

Therefore; the valve stem H2 is movedto the. right against the force of spring IZI, andopens the valve I-I 3 tdprovide'an additional supply of 7 fuel tov the engine in order that the engine: may

accelerate more quickly in of the'thro'ttles. 7 It has been foundthat-"the additional supply response. tomovement A' compression spring N16 is retained between the disc I and A valve quite rapid, and supplies an additional amount 16 is above atmospheric; it will be seen that when p tie position. The action of the regulator Illis of fuel to the engine almost immediately upon opening of the throttles. .This supply stops; however, as soon as the pressure conditions on. the opposite sides of the diaphragm I II have become equalized through the restriction I20. It has 7 been found with a device of this type the extra supply of fuel may be out oil before the engine has actually accelerated to the desired speed". To

overcome this condition there is provided a sec-- ondary acceleration responsive regulator shown at I25 in the drawing. 1

The secondary regulator I25 comprises'a casing divided by a flexible diaphragm I26 into two expansible chambers, The chamber to-the right 7 I of the diaphragm I26 is connected through' a conduit I2'I to the outlet I3 of air passage H,

downstream from the throttles I02. The diaphragm I26'carri'es a'disc valve H8 at its central portion. 7 nular. seat I39, which is fixed to the body of the carburetor Ill; The space inside the annular seat ISO is connected by means of a conduit I3I and a restriction'I32 to the interior of chamber in the fuel regulator H. The conduit I3I is in communication with the conduit 68 through a check valve 533. When-the throttles I02 are partially closed, the pressure inithe chamber to the right of diaphragm I 25 is low compared to the fuel pressure in the chamber 45' and inthe conduit 63. Therefore, at such times check valve I33 opens, 'andfuel flows into the chamber at the left of diaphragm I26. The fuel is stored in this chamber; When an opening movement is given-to the throttles I82, the pressure downstream from the throttles increases and the diaphragm I23 moves to the left forcing the fuel stored in the left hand chamber through'thfe con-.

duit I3I and restriction I32 into thechamber 5' of the fuel regulator. It will be seen that this instriction I32 and. the dissipation of the increased pressure is delayed by the restriction 6 9,so that the increased pressure is maintained thereby over a periodof time considerably longer than that required to restore a constant pressure condition in the air passage II. The capacity of the secondary regulator I26 and the area of the restriction I32 may be so proportioned that this time delay is justsufiicient to complete the accelera- 7 7 tion of the engine to the final speeddesiredr 7 means forsupplying'liquid fuel to said chamber; a

means. for controlling the pressure. in saidzchame offfuelprovidedby'means'of theprlmary regulater-I I0 may not be suflicient-to accelerate the engine to the speed called for by the new-throt-r 7 5 While I have shown anddescribed certain. pre-- ferred embodiments of my invention, other medi a V flcations thereof will occur to those skilled in the art and I therefore intend that myinvention. shall be limited only by the appended claimsfli r. 7

- 'I claim as my invention: .5 r 7 I. In a fuel supply system for an internal com.- bustiori engine, a liquid fuel conduit, au a-h e in said fuel conduit,"meansresponsive to thefiow of combustionair to said engine andto the first of fuel thru said conduit for operating said valve to maintain a substantially constant fuel-mean" ratio; sai-d'valve operating means-including an r expansible. chamber having-a movable jwall,

her, and aconnectionbetween said wall andsai-d The valve I 28 cooperates with an an a throttle for controlling the flow of air to said engine, a pump operative to discharge fuel as an incident to an opening movement of said throttle, an inlet conduit for supplying liquid fuel to said pump, a discharge conduit for conveying fuel from said pump to said chamber, a fixed restriction in said pump discharge conduit for retarding the increase in pressure in said chamber and the consequent opening movement of said valve in response to operation of said pump, an outlet passage for said chamber, and a fixed restriction in said outlet passage for delaying restoration of said valve to its normal operating condition following an operation of said pump.

2. In a fuel supply system for an internal combustion engine, a liquid fuel conduit, a valve in said fuel conduit, a metering restriction in said conduit, means for operating said valve in response to the fuel pressure differential across said restriction, said valve operating means including a pair of expansible chambers separated by movable wall means, means connecting said chambers to said conduit on opposite sides of said restriction, and a connection between said wall means and said valve for moving said valve in an opening direction when the pressure in the one of said chambers connected to the downstream side of said restriction increases, a throttle for controlling the fiow of air to said engine, a pump operative to discharge fuel as an incident to an opening movement of said throttle, an inlet conduit for supplying fuel to said pump, a discharge conduit for conveying fuel from said pump to said one chamber, a fixed restriction in said pump discharge conduit for retarding the increase in pressure in said one chamber and the consequent opening movement of said valve in response to operation of said pump, an outlet passage for said one chamber, and a fixed restriction in said outlet passage for delaying restoration of said valve to its normal operating condition following an operation of said pump.

3. A fuel supply system for an internal combustion engine, comprising a liquid fuel conduit, a valve in said fuel conduit, means responsive to the flow of combustion air to said engine and to the flow of fuel thru said conduit for operating said valve to maintain a substantially constant fuel-air ratio, and Valve operating means including an expansible chamber having a movable wall, means for supplying liquid fuel to said chamber, means for controlling the pressure in said chamber, and a connection between said wall and said valve for moving said valve in an opening direction when the pressure in said chamber increases, a throttle for controlling the flow of air to said engine, a pump operative to discharge fuel as an incident to an opening movement of said throttle, a discharge conduit for conveying fuel from said pump to said chamber,

an inlet conduit for supplying fuel to said pump on its intake stroke from said fuel conduit so that said intake stroke does not decrease the pressure in said chamber, a fixed restriction in said pump discharge conduit for retarding the increase in pressure in said chamber and the consequent opening movement of said valve in response to operation of said pump, an outlet passage for said chamber, and a fixed restriction in said outlet passage for delaying restoration of said valve to its normal operating condition following an operation of said pump.

4. A carburetor for an internal combustion engine, comprising a conduit for combustion air flowing to said engine, means associated with said air conduit for producing two unequal pressures whose difference is a measure of the rate of fiow of air therethru, a conduit for fuel flowing to said engine, a metering restriction in said conduit for regulating the flow of fuel therethru in accordance with the fuel pressure differential established thereacross, a valve in said fuel conduit for varying said fuel pressure differential, means for operating said valve including four expansible chambers separated by concurrently movable wall structures, means operatively connecting said wall structures and said valve, means for communicating said two unequal air pressures to two of said chambers so that the difference of said two unequal pressures acts on said valve in an opening direction, means for communicating the fuel pressure on the upstream side of said metering restriction to a third of said chambers, means for communicating the fuel pressure on the downstream side of said metering restriction to the fourth of said chambers said fuel pressure differential acting thru said third and fourth chambers on said valve in a closing direction, a restricted passage connecting said third and fourth chambers for supplying fuel to said fourth chamber, said restricted passage cooperating with said last-mentioned communicating means to provide circulation of fuel thru said fourth chamber, a throttle for controlling the flow of air to said engine, a pump operative to discharge fuel as an incident to an opening movement of said throttle, a discharge conduit for conveying fuel from said pump to said fourth chamber, and a fixed restriction in said lastmentioned communicating means, said fixed restriction and said restricted passage cooperating to delay restoration of said valve to its normal operating condition following an operation of said pump.

SCOTT F. HUNT.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,858,835 Mabee et al May 17, 1932 2,088,464 Chandler et al July 27, 1937 2,224,472 Chandler Dec. 10, 1940 2,277,930 Mock et a1 Mar. 31, 1942 2,316,300 Udale Apr. 13, 1943 2,328,604 Bicknell Sept. 7, 1943 FOREIGN PATENTS Number Country Date 487,176 Great Britain June 16, 1938 521,230 Great Britain May 15, 1940 542,761 Great Britain J an. 27, 1942 

